This invention relates to semi-conductor device packages and more specifically to an improved semiconductor device package assembly for improving overall package performance.
In recent years, electronic devices have been miniaturized and decreased in overall thickness and the semi-conductor devices and IC chips employed in these devices are provided with high packaged density. One conventional technique for assembling integrated circuit chips is the so-called TAB for tape automated bonding schemes. The TAB technique makes it possible to obtain fine, multiple lead patterns with a variety of pattern design variations.
According to the TAB technique, a copper foil is bonded to a polyimide film substrate and etched to a prescribed pattern, forming leads. The inner lead portions of the leads have tips that protrude over an opening at the central portion of the film substrate, and the tips are connected by gang bonding to an IC chip arranged with its active face down above the opening. The final packaging is realized using a potting resin sealing technique.
FIGS. 1 and 2 illustrate the conventional TAB technique as described above. In FIG. 1 a polyimide film substrate 103 is shown to form a hollow square. The copper foil which has been bonded to the film substrate 103 has also been etched into a pattern of leads 102. An inner portion of the metal lead portions 104 extends beyond the edge of the substrate film and into the aperture 101. A die is then attached to the inner lead portions 104, overlapping the central aperture 101.
During the initial manufacturing steps which lead to the TAB assembly shown in FIG. 1, the substrate film and the copper foil additionally occupy the area where aperture 101 is shown to be. However, this central portion of substrate film and copper foil is removed during the tape manufacturing process.
There are a number of reasons why the central portion is removed. First, the central portion is removed to facilitate the subsequent attachment of the die. The tape and the copper foil make it difficult to visually align the inner bonding leads to the corresponding pads on the die. In addition, the central portion also makes it more difficult to bond the leads to the die. By removing the central portion, the center part of the TAB assembly is opened up, facilitating both the alignment and bonding processes. Second, the central portion interferes with the encapsulation process. Since the conventional TAB technique includes the step of encapsulating the active surface of the die and the inner lead bonding areas (discussed below), the central portion only serves to interfere with this process, and therefore is removed. The result of removing the central portion of tape and copper foil is the aperture 101 illustrated in FIG. 1.
Once the die has been attached to the TAB assembly, it is then encapsulated as illustrated in FIGS. 2A and 2B. FIG. 2A is a view of the TAB assembly from the opposite side of that of FIG. 1. The encapsulation area 201 is shown to completely encapsulate the active surface of the die as well as the inner lead bonding areas 104. A clearer picture is provided in FIG. 2B, which is a cross-sectional view of the Figure of 2A taken along the line 2B. In FIG. 2B, it can be seen that the encapsulation material 201 encapsulates the active surface of the die 150, the inner bonding lead portions 104, and the electrically conductive bumps 155 which are used to connect the inner bonding lead portions 104 to bond pads on the die.
Although the above described TAB technique is widely used in the semi-conductor packaging industry, it is not without its limitations and drawbacks. For example, one such drawback is the rupturing of inner lead portions 104 from the die due to stress caused by the heating and cooling of the encapsulating material. During temperature cycle testing and during operation of the TAB package in various environments, the encapsulation material, the metal leads, and the die are each subjected to an extreme range of temperatures, which causes them to expand and contract. Such expansion and contraction place stress upon the inner lead portions 104 which, in turn, eventually causes the leads to break or rupture from the die.
One purpose of the encapsulation process is to provide scratch protection for the active surface of the die as well as for the inner lead bonding areas. However, despite the advantage of providing scratch protection, another drawback of this process is that the encapsulation material prevents and/or hinders the dissipation of heat from the active surface of the semiconductor die. Yet another drawback is that, in some encapsulation processes (such as potting, for example), the encapsulation material does not provide a desirable surface for marking and identifying the package.
In light of these drawbacks, therefore, one objective of the present invention is to provide scratch protection for the active surface of the die and for the inner lead bonding areas without hindering the dissipation of heat from the active surface of the die. Another objective of the present invention is to reduce the stress on the inner lead bonding areas while simultaneously providing scratch protection to these areas. Yet another objective of the present invention is to improve the overall performance of the TAB package.